Interactions of cocaine with primary and secondary recognition sites on muscarinic receptors

Donna D. Flynn, Asmita A. Vaishnav, Deborah C Mash

Research output: Contribution to journalArticle

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Abstract

Several lines of evidence have suggested that muscarinic receptors may possess more than one ligand binding site. In this study, the interactions of cocaine with primary and secondary (allosteric) sites on muscarinic receptors in membrane homogenates from post-mortem human brainstem were examined. (-)-Cocaine inhibited the binding of the tritiated muscarinic antagonists N-methylscopolamine (NMS) and pirenzepine to an apparent single class of sites, with Ki values of 200-300 μM. The binding of the muscarinic agonist [3H]oxotremorine-M was inhibited with a similar Ki value (200 μM). (+)-Cocaine, although not the naturally occurring stereoisomer, was 10-20-fold more potent than (-)-cocaine in competing for binding to the primary muscarinic recognition site. The binding of cocaine was unaffected by guanine nucleotides or N-ethylmaleimide, consistent with its purported action as a competitive antagonist. Cocaine was not selective for muscarinic receptor subtypes. Rosenthal analysis of the [3H]NMS saturation binding data in the presence of increasing concentrations of either (-)-cocaine or (+)-cocaine indicated that both isomers produced an apparent competitive-like reduction in the [3H]NMS affinity. Schild regression analysis of the saturation binding data resulted in curvilinear plots suggestive of cooperative or allosteric interactions of (-)-cocaine with the [3H]NMS-labeled receptors. The effects of (-)-cocaine on the kinetics of [3H]NMS binding were consistent with an allosteric interaction with the receptor. Increasing concentrations of cocaine markedly slowed the rate of [3H]NMS dissociation from the primary recognition site. The allosteric modulation of [3H] NMS binding by (-)-cocaine was abolished with increasing ionic strength. Taken together, these data demonstrate that (-)-cocaine interacts with primary and allosteric recognition sites on muscarinic receptors.

Original languageEnglish
Pages (from-to)736-742
Number of pages7
JournalMolecular Pharmacology
Volume41
Issue number4
StatePublished - Apr 1 1992

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Muscarinic Receptors
Cocaine
N-Methylscopolamine
Allosteric Site
Pirenzepine
Muscarinic Agonists
Stereoisomerism
Ethylmaleimide
Muscarinic Antagonists
Guanine Nucleotides
Osmolar Concentration
Cholinergic Agents
Brain Stem
Binding Sites
Regression Analysis

ASJC Scopus subject areas

  • Pharmacology

Cite this

Interactions of cocaine with primary and secondary recognition sites on muscarinic receptors. / Flynn, Donna D.; Vaishnav, Asmita A.; Mash, Deborah C.

In: Molecular Pharmacology, Vol. 41, No. 4, 01.04.1992, p. 736-742.

Research output: Contribution to journalArticle

Flynn, Donna D. ; Vaishnav, Asmita A. ; Mash, Deborah C. / Interactions of cocaine with primary and secondary recognition sites on muscarinic receptors. In: Molecular Pharmacology. 1992 ; Vol. 41, No. 4. pp. 736-742.
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